1. Field of the Invention
This invention relates to computer-aided design systems, i.e., computer controlled graphics and particularly to computer-aided design applications where one of many drawings, views, patterns, lines, or points can be selected for modification by the user. For purposes of explanation, computer-aided drawings comprise a hierarchy, the top being a drawing, a drawing being comprised of one or more views, a view being comprised of one or more patterns, a pattern being comprised of one or more lines, and lines being defined by points.
An entity is a member of any level in the hierarchy.
The subject matter includes cursor mark position control having a manual means which determines the position and controls particular energization of a display element to which the control by the input means is directed.
2. Description of Related Art
In computer controlled graphics, a cursor is an on-screen symbol used to supply feedback to the user by visually indicating the position and set membership of selected displayed entities. A moveable cursor can be used to select entities for purposes of altering the displayed graphics.
Where many entities appear on the screen, e.g., boxes, circles, nuts and bolts, and polygons, selecting the desired entity by moving a selection device to the proximity of the entity to be identified is not an easy process. The mathematical computations require more time because of the increase in the number of points and lines to be taken into account.
The selection devices for computer-aided design (CAD) applications include styli on digitized tablets, mouse, light pens, or joy sticks. Such devices function to return a set of x,y coordinates that indicate where the selection device specifying the cursor has been positioned with respect to the system of coordinates used in the display system. When trying to select a given point or line with a selection device, it is difficult to place the selection device exactly at the x,y coordinates of the entity to be selected.
Closely spaced entities increase the difficulties of selecting the desired entity. Correlation, as used herein, is the ability to associate a selected x,y coordinate to a screen entity without ambiguity. Existing techniques use mathematical algorithms for calculating whether each individual vector displayed on a graphic screen is correlated to the x,y position returned by an input device. As the number of vectors displayed on the screen increases, the time required to correlate increases proportionately, since more calculations have to be made on more vectors until the correct vector is identified.
When CAD workstations were connected to large main frame processing units, which were very fast, the time required for the calculations was short. Using such CAD applications on smaller processors, such as personal computers, requires longer periods of time for correlation.
A substantial amount of time is required to correlate graphic data on a CRT screen, and when a large amount of geometry is displayed, the correlation calculations use a large amount of time. Complex geometry in many systems cannot be conveniently edited because of the amount of time required. In graphic programs run on personal computers, correlation usually degrades performance of the system.
The invention to be described has a correlation time, independent from the amount of data and provides almost instantaneous correlation of the selected entity, even when used with slow processors. The invention to be described is device independent and can be adapted for CADAM, e.g., trapping.
Low cost raster devices have graphic hardware that are not capable of differentiating between a single line or multiple lines occupying the same end points. Therefore, in the case of multiple lines having the same x,y coordinates of end points, if one line is to be erased, the system cannot determine whether there are lines beneath it, leaving a space where the line should have been. The effect is that the screen does not display the actual information relating to the drawing. To restore the lines beneath a deleted line, the system has to redraw the display, which is a slow process and requires and operator to constantly work with inaccurate information, constantly selecting the redraw operation. The invention eliminates the above described problems.
U.S. Pat. No. 3,997,891 describes a light pen detection system for detecting the character display are on a cathode ray tube (CRT) display. The character near the pen is marked and, if not the desired one, the detection process continues until an indication is provided indicating that the correct character has been detected. The system according to this patent responds to light on the detecting surface of the pen which means that the selected character is the one having a portion thereof at the point on the display where the pen is positioned.